Hard disk drives are common information storage devices essentially consisting of a series of rotatable disks that are accessed by magnetic reading and writing elements. These data transferring elements, commonly known as transducers, are typically carried by and embedded in a slider body that is held in a close relative position over discrete data tracks formed on a disk to permit a read or write operation to be carried out. In order to properly position the transducer with respect to the disk surface, an air bearing surface (ABS) formed on the slider body experiences a fluid air flow that provides sufficient lift force to “fly” the slider and transducer above the disk data tracks. The high speed rotation of a magnetic disk generates a stream of air flow or wind along its surface in a direction substantially parallel to the tangential velocity of the disk. The air flow cooperates with the ABS of the slider body which enables the slider to fly above the spinning disk. In effect, the suspended slider is physically separated from the disk surface through this self-actuating air bearing. The ABS of a slider is generally configured on the slider surface facing the rotating disk, and greatly influences its ability to fly over the disk under various conditions. For a typical disk drive (−160 GB/platter) on the market, the distance between a magnetic head and the media is less than 10 nm. In order to correctly read and write data, it is essential that the sliders fly stably over the magnetic recording media during reading and writing.
There are currently two types of drive designs on the market. The first is a Load/Unload (LUL) design, where sliders stay on a ramp that is outside the perimeter of the magnetic disk when no reading or writing is performed. The second is a Contact Start Stop (CSS) design, where the sliders park on the magnetic media at the innermost diameter (also referred to as the Landing Zone) of the magnetic disk when no reading or writing is performed. Once the disk stops rotating, the slider comes to rest on the surface of the disk. When the rotation of the disk begins again, the air-bearing is formed once again and the slider separates from the disk. In order to reduce friction between the slider and the disk, a very thin layer of lubricant on the order of a few nanometers, is applied to the surface of the disk. A common problem with the operations of CSS drives is the starting friction (“stiction”). Stiction is caused by viscous lubricant between the slider and the disk. In some cases, especially in a humid environment, the slider is held down strong enough that the disk fails to rotate. To correct this problem, pads are introduced onto the surface of the slider to reduce the area of contact between the slider and the disk. The pads are extremely tall to minimize the stiction problem described above.
The stiction consideration for CSS drives with padded sliders requires that the angle between the disk and backplane of the slider (commonly referred to as the “pitch angle” or “pitch”) be above a certain value such that there is no pad contact. As a result of this need, it is not uncommon for a CSS drive to have a high flying pitch angle of greater than 150 microradians.
It is further realized that the flying pitch of a conventional ABS design for a CSS drive is not uniform across the diameter of a magnetic disk. Due to the greater tangential velocity, and hence greater air flow, at the outer diameter of the disk (OD), the pitch angle at the OD of the disk is usually much higher than that in the start stop zone.
FIG. 1 shows a slider body 100 with a high pitch angle and some particles 140a-b flying between the slider 100 and disk 120. The slider has a magnetic sensor (i.e. a read/write element) 150 for reading and writing at the trailing edge. At higher pitch angles, more particles are likely to pass through the magnetic sensor 150 which can cause critical reliability issues such as thermal asperity (TA) or even physical damage to the read/write element 150. Thermal asperity occurs when particles on the disk surface change the resistance between the read/write element and the disk surface, thus causing read/write errors. Physical damage to the read/write element 150 can occur when large particles 140b make contact with magnetic sensor 150. Repeated impact with particles in the disk drive can degrade or even permanently damage the read/write element 150.
Another important reliability issue is the uneven flying heights (FH) at high altitudes due to uneven flying pitch. The lift force experienced by the ABS is a product of both air density and the amount of air flow. Therefore, a conventional ABS design will have a lower flying height in the less-dense air of high altitudes than it has at sea level. This can be especially problematic at the inner diameter (ID) where there is less air flow to lift the ABS. The FH at the inner diameter is usually low with a low flying pitch, which can result in head-disk contact or failure at high altitude. Reducing altitude FH sensitivity is one way to deal with this difficulty. However, this approach does not solve the issues associated with pitch drop at certain tracks. For example, the FH at the sensor area may change only slightly, but the flying pitch could still drop significantly, moving the minimum FH location to the leading edge of the ABS (such as anti-stiction pads), causing altitude failure at the inner radius of the disk. Therefore, a high enough pitch angle should be maintained at the ID.
In view of these reliability issues associated with current CSS drives with high pitch ABS designs, the present invention proposes using a pitch ladder and an air channel for controlling the pitch profile of CSS drives.